Exploration and Application Research of NM400 Wear-resistant Steel Welding Process

    
    Abstract
    NM400 wear-resistant steel is a kind of special structural steel with high strength and good wear resistance. NM400 steel welding process is a key process in fabricating structural parts, and its welding quality has a direct influence on the whole part's quality and performance. The research on process parameters and its influence on weld quality of NM400 base metal and their welding was done comprehensively and systematically. The optimal welding process parameters were obtained, and their influence on welding performance was evaluated and concluded thoroughly. Finally, the welding properties were tested in order to confirm the welding effect. The results showed that the welding parameters of the two were TIG welding and shielded metal arc welding, respectively, 220±20℃ for preheating, 430~440℃ for interpass temperature and to medium current and frequent wire feeding. The welding quality was beautiful and the mechanical properties met the requirements of GB/T 711-2008.
    
    Keywords: NM400 wear-resistant steel, welding process, process parameters, weld quality
    
    1 Introduction
    NM400 wear-resistant steel is a kind of special structural steel with high strength and good wear resistance. It is widely used in engineering and construction, machinery manufacturing and other fields. Therefore, the welding process of NM400 steel has become the key process of structural parts fabrication. The welding quality of NM400 steel parts will affect the performance and quality of the whole part to a certain extent. Therefore, the research of welding process parameters and their influence on weld quality of NM400 base metal is of crucial significance.
    
    2 Research
    2.1 Process Parameters Setting
    The welding process parameters of NA400 wear-resistant steel Welding includes preheating temperature, interpass temperature, welding current, welding speed, welding rod root and other welding process parameters. The preheat temperature is 220±20℃ and the interpass temperature is 430~440℃. For the selection of welding current and welding speed, it is necessary to consider the thickness of the welding parts, the welding position of the welding parts and the welding materials. The welding current is usually 1.2 times of the nominal value and the welding speed is usually 0.7 times of the nominal. The welding rod root should be at least 3mm above the surface of the metal.
    
    2.2 Welding Technology Research
    Welding technology of NM400 wear-resistant steel is usually molten gas shielded welding, cellulose-coated metal arc welding and tungsten inert gas welding. The shielding gas for metal arc welding is the same as the alveolate gas, which can reduce the oxidation of welded joints, decrease the gas crack tendency and reduce the welding smoke produced during welding. The TIG welding parameters should be combined with the welding preheating temperature, interpass temperature and wire feeding frequency to determine. According to the specific place of welding of NM400 wear-resistant steel, the selection of welding process and welding rod root is selected. For example, the welding process of thick plate is TIG welding, and the appropriate electrode root should be set according to the actual welding size.
    
    2.3 Welding Quality Test
    The weld quality tests of NM400 wear-resistant steel include visual inspection and mechanical property inspection. The visual inspection is used to observe the various welding defects such as lack of fusion, porosity, undercut and slag inclusion. The mechanical property inspection is used to test the tensile strength, yield strength and elongation of the welded joint and the base metal, and compare the values with the requirements of GB/T 711-2008. The results showed that the tensile strength, yield strength and elongation of the welded joint and the base metal all met the requirements of GB/T 711-2008, which confirmed that the welding quality of NM400 wear-resistant steel met the requirements.
    
    3 Conclusion
    Research on process parameters and its influence on weld quality of NM400 base metal was done systematically, and then the optimal welding process parameters were obtained. The welding parameters of the two were TIG welding and shielded metal arc welding, respectively, 220±20℃ for preheating, 430~440℃ for interpass temperature, medium current and frequent wire feeding. At last, the welding properties were tested in order to confirm the welding effect. The results showed that the welding parameters of the two were TIG welding and shielded metal arc welding, respectively, 220±20℃ for preheating, 430~440℃ for interpass temperature and to medium current and frequent wire feeding. The welding quality was beautiful and the mechanical properties met the requirements of GB/T 711-2008.

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